title: Use of high-pressure CO2 for concentrating CrVI from electroplating wastewater by Mg-Al layered double hydroxide.
abstract: The desorption of Cr(VI) from Cr(VI)-adsorbed layered double hydroxide (Cr(VI)-LDH) and the recycling of LDH adsorbent are the bottlenecks that limit the practical application of LDH in treating Cr(VI)-containing industrial wastewater. Given the strong affinity of LDH for CO2, we studied desorption and enrichment of Cr(VI) from Cr(VI)-LDH as well as recycling of LDH in the presence of high-pressure CO2. Results showed that Cr(VI) solution with concentration of 500 mg/L could be enriched more than 20 times in each adsorption-desorption cycle. The regenerated LDH maintained the layer structure and the sheets as revealed by XRD and TEM patterns. FT-IR data showed CO2 formed HCO3(-) at high pressure. The transformation from CO2 to HCO3(-) followed by the anion-exchange with CrO4(2-) was the critical factor for Cr(VI) desorption and LDH regeneration. A pilot-scale experiment was carried out with 20 L Cr(VI)-containing electroplating wastewater. The concentration of the desorbed Cr(VI) solution could reach up to 10000 mg/L, which could be used in electroplating after appropriate adjustment. The main advantages of this method are high concentration of Cr(VI), direct reuse of enriched Cr(VI), and efficient regeneration of LDH adsorbent. This method showed promises in recycling Cr(VI) and regenerating LDH in treating industrial wastewater.
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences , Fuzhou, Fujian 350002, China.
authors.forename: Xiangying
authors.initials: X
authors.lastname: Lv
authors.forename: Zhi
authors.initials: Z
authors.lastname: Chen
authors.forename: Yongjing
authors.initials: Y
authors.lastname: Wang
authors.forename: Feng
authors.initials: F
authors.lastname: Huang
authors.forename: Zhang
authors.initials: Z
authors.lastname: Lin